A single modern semiconductor integrated circuit (IC), commonly referred to as a chip, often contains both one or more analog circuit blocks and one or more digital circuit blocks. Combining analog circuits and digital circuits within the same IC is commonly called a system on a chip (SoC). An IC that implements an SoC provides significant advantages for the electronic device that includes such a chip. These advantages include: increased speed and reduced power, because more of the electronic device's signals stay within the SoC IC. These advantages also include reduced cost and reduced space requirements, because more of the electronic device is implemented within fewer SoC ICs.
However, implementing both an analog circuit and a digital circuit within the same IC poses very substantial design challenges. One of the foremost among these challenges is that electronic noise generated in the digital circuit generally transfers over to the analog circuit. Such electronic noise can easily interfere with the proper operation of the analog circuit. Such a noise transfer is also known as a coupling or an injection.
A digital circuit generally operates based on large swings in the voltages of its signal wires and clock wires. These large swings can produce substantial electrical noise in the power supply lines (i.e., Vdd lines), in the signal ground lines (i.e., Vss lines), and in the substrate of the IC (i.e., the package ground).
Digital circuits are generally more immune to electrical noise than are analog circuits. Thus, such noise is not usually enough to disrupt the operation of other digital circuits even if they are nearby. In contrast, analog circuits often operate with signals where relatively small voltage swings can be of crucial significance. Thus such noise may be enough to disrupt the proper functioning of an analog circuit even if a substantial distance separates the location of the analog circuit from the location of the digital circuit.
A SoC IC may provide a digital Vdd and a digital Vss that are respectively kept separate from an analog Vdd and an analog Vss. However, a single IC must be implemented using a single substrate which is electrically not an insulator.
Thus, there is a need for a system that reduces transfer of electronic noise from a digital circuit to an analog circuit within the same IC, where the transfer is via the substrate. There is also a need for a method of manufacturing such a system.